Please help me get a Oxygen concentrator

Hi my name is ,, Sherry, I have a hole in my heart, so I've been on Oxygen for the past year. I have been limited to where I can go and how long I can be there. So I have been trying to get a portable Oxygen concentrator. I use one size D oxygen cylinder per every 4 hours, if I go anywhere longer than 4hours I have to carry 2 cylinders or more, which I can only 1. I push around a cart to have 2 or more cylinders. This limits my life from doing what I do and Volunteering at the Greeley Senior center. The Doctor said yes I need a portable Oxygen concentrator, which I can't afford. I have been trying to get one through my oxygen company for about a year. I have heard about every excuse, to why I can't get it. So Please help me purchase a portable Oxygen concentrator to get my life back.